Modified retinoid compounds and their uses

ABSTRACT

A method of minimizing or reducing the toxicity of a retinoid having a free carboxyl group and the resulting modified retinoids are described. The method comprises the step of esterifying the carboxyl group of the retinoid with a highly sterically hindered compound, which is preferably a secondary or tertiary alcohol. The resulting retinoid esters are rendered much less toxic than the starting or parent retinoid. This process provides a retinoid ester analog of reduced toxicity so that it may be administered orally with minimal side effects and with a much greater therapeutic window. The modified retinoid compounds are useful in the treatment and prophylaxis of all diseases and disorders where retinoid compounds have been shown effective.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is based on and claims priority from provisionalpatent Application No. 60/440,683 filed on Jan. 17, 2003.

BACKGROUND OF THE INVENTION

[0002] The present invention is directed toward retinoids, and moreparticularly to a method of reducing the toxicity of retinoids andmodified retinoids having reduced toxicity.

[0003] All trans-retinol, the major circulating form of vitamin A, isconverted in the body to retinaldehyde and finally to all-trans-retinoicacid (atRA) (Blomhoff et al., 1992, Annu. Rev. Nutr. 12:37-57). atRAserves as the active form of vitamin A in cellular differentiation andgrowth, and embryonic development, whereas the aldehyde serves as theactive form in the visual cycle (Palczewski and Saari, 1997, Curr. Opin.Neurobiol. 7:500-504). It is also believed that atRA serves as theactive form in the reproductive functions of vitamin A (Clagett-Dame andDeLuca, 2002, Annu. Rev. Nutr. 22:347-381).

[0004] atRA, in addition to being a functionally active form of vitaminA, is also the parent of a family of drugs used both topically andorally for the treatment of a number of skin conditions (Ellis andKrach, 2001, J. Am. Acad. Dermatol. 45:S150-S157; Zouboulis, 2001, SkinPharmacol. 14:303-315). Furthermore, it and some of its isomers arebeing considered as chemo-preventive agents, for example in epithelialtumors, and may also serve as a therapy for certain types of leukemias(Fenaux and Degos, 2000, Leukemia 14:1371-1377). atRA is believed tofunction by binding to a series of retinoic acid receptor subtypes, α, βand γ, that also vary in sequence due to differences in promoter usageand splicing (Chambon, 1996, FASEB J. 10:940-954). atRA and its analogsare believed to act through a nuclear receptor (RAR) to activate orsuppress target genes responsible for its actions (Clagett-Dame andPlum, 1997, Crit. Rev. Euk. Gene Exp. 7:299-342; McCaffery and Dräger,2000, Cytokine Growth Factor Rev. 11:233-249). atRA is formed inregulated quantities because it is extremely potent and readilyactivates the retinoic acid receptors (Duester, 2000, Eur. J. Biochem.267:4315-4324). atRA is also rapidly metabolized so that its lifetime isrelatively short (Roberts and DeLuca, 1967, Biochem. J. 102:600-605).

[0005] Because it is immediately active, pharmacological amounts oforally administered RA isomers have very serious side effects (Armstronget al., 1994, in The Retinoids, pp. 545-572; DiGiovanna, 2001, J. Am.Acad. Dermatol. 45:S176-S182). Among them are frank toxicity resultingin weight loss, inanition, eye encrustation, and bone loss. Common sideeffects with pharmacological use of 13-cis RA (isotretinoin), a majororally administered form of RA, includes mucocutaneous toxicity andhyperlipidemia (Ellis and Krach, 2001, J. Am. Acad. Dermatol.45:5150-5157). An even more serious problem is that RA isomers havesignificant teratogenic activity in pregnant mammals (Collins and Mao,1999, Ann. Rev. Pharmacol. 39:399-430; Nau, 2001, J. Am. Acad. Dermatol.45:S183-S187). These side effects have been a serious limitation to theuse of oral retinoids in therapy. Although topically applied retinoidscarry little teratogenic liability (Nau, 1993, Skin Pharmacol.6:535-544; Buchan et al., 1994, J. Am. Acad. Dermatol. 30:428-434; Chenet al., 1997, J. Clin. Pharmacol. 37:279-284), there are othertoxicities associated with this route of administration that limit theiruse including skin irritation (Orfanos et al., 1997, Drugs 53:358-388).A major reason for both oral and topical toxicity is that the retinoidsare totally and immediately available upon administration. A processwhereby a retinoid can be made available in vivo more slowly and morecontinuously would avoid peaks and valleys in the availability of theretinoid thereby providing an effective in vivo level of the compoundover a more prolonged period of time and also avoiding or substantiallyreducing the toxicities that often result from the sudden availabilityof excessive amounts of the substance.

SUMMARY OF THE INVENTION

[0006] The present invention provides a method for modulating andregulating the in vivo activity of biologically active retinoidcompounds, such as all-trans-retinoic acid. More specifically, thisinvention provides modified retinoid compounds that exhibit a desirableand highly advantageous pattern of biological activity in vivo, namely,the more gradual onset and more prolonged duration of activity relatingto cell proliferation, cell differentiation and morphogenesis. As aconsequence of such advantageous properties, these compounds exhibitminimal or at least substantially reduced toxicity as compared to thestarting or parent retinoids and thus represent novel therapeutic agentsthat may be incorporated into a pharmaceutical composition containing apharmaceutically acceptable excipient for the treatment and prophylaxisof all diseases and disorders where retinoid compounds have been showneffective, such as proliferative skin disorders characterized byabnormal cell proliferation or cell differentiation e.g. dermatitis,eczema, keratosis, acne and psoriasis. They should also be especiallyuseful for the treatment of neoplastic diseases such as skin cancer,colon cancer, breast cancer, prostate cancer, lung cancer, ovariancancer, neuroblastoma, and leukemia as well as for the treatment of skinconditions such as wrinkles, lack of adequate skin firmness, lack ofadequate dermal hydration, and insufficient sebum secretion.

[0007] Structurally, the key feature of the modified retinoid compoundshaving these desirable biological attributes is that they are esterifiedwith a highly sterically hindered compound, preferably an alcohol.Depending on various structural factors—e.g. the type, size, structuralcomplexity—of the substituents on the attached alcohol, thesederivatives are thought to modulate the biological action of theretinoid by hydrolyzing to the retinoid at different rates in vivo, thusproviding for the “slow release” of the retinoid which results in a muchgreater therapeutic window for the biologically active retinoid in thebody.

[0008] The in vivo activity profiles of such compounds can, of course,be further modulated by the use of mixtures of derivatives (e.g.mixtures of different retinoid ester derivatives) or the use of mixturescomprising one or more retinoid derivative together with one or moreunderivatized retinoid compounds or in combination with otherbiologically active compounds such as vitamin D compounds.

[0009] It is important to stress that the critical structural feature ofthe retinoid derivatives identified above is the presence of a highlysterically hindered group attached to the carboxyl group of the retinoidmolecule. The presence of a highly sterically hindered group at thatposition imparts on the resulting derivatives the desirable slow releasebiological activity profile mentioned above. The fact that theintroduction of a highly sterically hindered group at the free carboxylgroup of the retinoid molecule markedly modulates the in vivo biologicalactivity pattern of the resulting derivative was not appreciatedpreviously. The realization of the importance of this specificmodification, and the demonstration of its marked and highly beneficialbiological effects form the basis of this invention.

[0010] Initially three sterically hindered alcohol esters of atRA weresynthesized, namely, the t-butyrate ester (retinoyl t-butyrate, alsoreferred to in this application as t-butyl-RA) as well as the pinacolester (retinoyl pinacol) and the cholesterol ester (retinoylcholesterol). The results of biological testing reveal that thet-butyrate ester is as active in vivo when given orally as is atRA. Yetwhen t-butyl-RA was given in large excess, it proved to be relativelynon-toxic and, furthermore, a 10-fold higher dose of this compoundcompared to atRA was required to produce equivalent teratogenic effects.The pinacol ester appeared nearly as active as atRA in supporting growthof vitamin A-deficient rats compared to atRA. The toxicity of thiscompound was not tested but likely it also represents a very non-toxicform of atRA. The cholesterol ester was less effective in supporting thegrowth of vitamin D-deficient rats, but was till superior to vehicle inthis activity.

[0011] Since almost all of the active ligand-specific retinoids havefree carboxyl groups, esterifying them with a sterically hinderedalcohol can be used to slow down the biological actions of theretinoids, thereby markedly reducing their toxicity at pharmaceuticallyacceptable doses and providing a much greater therapeutic window. Thepresent invention thus provides a method whereby a retinoid can berendered much less toxic, by derivatization with a highly stericallyhindered compound, preferably an alcohol, so that the ester will beslowly hydrolyzed in the body to the retinoid. This would allow theretinoid derivative, i.e. the retinoid pro-drug, to be administered withmuch less danger of bone loss, weight loss, inanition, mucocutaneousirritation, hyperlipidemia and teratogenicity, which are side effectstypically associated with oral retinoid use; or skin irritation as canoccur with the use of topically applied retinoids.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a graph illustrating growth of vitamin A-deficient ratsgiven oil vehicle, or 83 pmole/day of either all-trans-retinoic acid(atRA) or t-butyl-retinoic acid (t-butyl-RA) for five days;

[0013]FIG. 2 is a graph illustrating growth of vitamin A-deficient ratsgiven oil vehicle or 166 pmole/day of either all-trans-retinoic acid(atRA) or t-butyl-retinoic acid (t-butyl-RA) for five days;

[0014]FIG. 3 is a bar graph summarizing the weight data illustrated inFIGS. 1 and 2;

[0015]FIG. 4 is a graph illustrating growth of vitamin A-deficient ratsgiven oil vehicle or 83 pmole/day of either all-trans-retinoic acid(atRA), the pinacol ester of atRA, or the cholesterol ester of atRA forfive days;

[0016]FIG. 5 is a graph illustrating the toxicity of all-trans-retinoicacid (atRA) versus t-butyl-retinoic acid (t-butyl-RA);

[0017]FIG. 6 is a graph similar to FIG. 5 illustrating the results of asecond independent study of the toxicity of all-trans-retinoic acid(atRA) versus t-butyl-retinoic acid (t-butyl-RA); and an oil vehicle;

[0018]FIG. 7 is a bar graph showing the toxicity of all-trans-retinoicacid (atRA) as illustrated by the reduction in testes weight of the ratsused to obtain the data of FIGS. 5 and 6; and

[0019]FIG. 8 is a bar graph illustrating the teratogenic activityexhibited by all-trans-retinoic acid (atRA) compared to the lack oftoxicity of t-butyl-retinoic acid (t-butyl-RA) at 0.1 mmole/kg.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention is directed toward a method of minimizingor reducing the toxicity of a retinoid having a free carboxyl groupcomprising the step of esterifying the carboxyl group with a highlysterically hindered compound, which is preferably an alcohol. Theresulting retinoid esters are rendered much less toxic than the startingor parent retinoid. This process provides a retinoid ester analog ofreduced toxicity so that it may be administered orally with minimal sideeffects and with a much greater therapeutic window.

[0021] Retinoic acid (RA) plays a fundamental role in cellproliferation, and cell differentiation and it may also preventmalignant transformation (Darmon, 1991, Sem. Dev. Biol. 2:219). Theeffects of RA and synthetic derivatives are mediated by two classes ofnuclear receptors, the retinoic acid receptors (RARs) which belong tothe erbA-related steroid/thyroid nuclear receptor superfamily and theretinoid X receptors (RXRs) which also belong to the same super familyof steroid/thyroid hormones. Retinoids are analogs of vitamin A. Any ofthe synthetic retinoids that activate RARs and RXRs and have a freecarboxyl group can be esterified in accordance with the present processto make them less toxic. In the present description, the term “retinoid”and/or “retinoid compound” refers to a class of compounds consisting offour isoprenoid units joined in a head-to-tail manner. All retinoids maybe formally derived from a monocyclic parent compound containing fivecarbon-carbon double bonds and a functional group at the terminus of theacyclic portion. The term vitamin A should be used as the genericdescriptor for retinoids exhibiting qualitatively the biologicalactivity of retinol. This term should be used in derived terms such asvitamin A activity, vitamin A deficiency, vitamin A antagonist, etc.Examples of retinoids useful in the present process include9-cis-retinoic acid, 11-cis-retinoic acid, 13-cis-retinoic acid,9,13-di-cis-retinoic acid, benzoic acid-terminated retinoids and theirheterocyclic analogs such as TTNPB, TTAB, Am80, Am580, SRI 1251,SR11247, CD666, CD367, chalcone-4-carboxylic acids,flavone-4′-carboxylic acids, etc. (Loeliger et al., 1980, Eur.J.Med.Chem-Dhim. Ther. 15:9), (Kagechika et al., 1989, J. Med. Chem. 32:834),(Dawson et al. 1995, J. Med. Chem. 38:3368) illustrated below as well as

[0022] napthalenecarboxylic acid-terminatedated retinoids such as TTNN,CD437, CD417 or adapalene (Dawson et al., 1983, J. Med. Chem. 26:1653),(Dhar et al., 1999, J. Med. Chem. 42:3602) and many other carboxylicacid retinoids (AGN 190299 or tazarotenic acid and R_(o) 10-9359 oracitretin).

[0023] Additional synthetic retinoids useful in the present method aredescribed and illustrated below as well as in Dawson et al, “SyntheticRetinoids and their Usefulness In Biology and Medicine,” Vitamin A andRetinoids, M. A. Livrea (ed.), pp, 161-196 (2000). See also: retinoidslisted in http://www.chem.qmul.ac.uk/iupac/misc/ret.html 5 as well as inArch. Biochem. Biophys., 1983, 224, 728-731; Eur. J. Biochem., 1982,129, 1-5; J. Biol. Chem., 1983, 258, 5329-5333; Pure Appl. Chem., 1983,55, 721-726; Biochemical Nomenclature and Related Documents, 2ndedition, Portland Press, 1992, pages 247-251. The following listcorrelates the structures hereinafter shown with its name and/or codenumber. Retinoid Structure Name/code number 3-1 trans-RA 3-2 9-cis-RA3-3 TTNPB/Ro13-7410 3-4 UAB8 3-5 CD367 3-6 SR11365 3-7 SR11256 3-8 Am5803-9 Am80 3-10 AGN 193836 3-11 CD2019 3-12 BMS188970 3-13 Ro48-2249 3-14TTNN/SR3957 3-15 BMS185282 3-16 BMS185283 3-17 BMS185354 3-18 SR112543-19 Ro44-4753 3-20 CD437 3-21 LGD100568 3-22 SR11217 3-23 LDG1069 3-24SR11246 3-25 SR11345 3-26 LDG100268 3-27 AGN 191701 3-28 AGN 192849 3-29HX600 nr⁶ Ro25-7386

[0024] The highly sterically hindered alcohols useful in the presentmethod comprise an alcohol selected from the group consisting ofsecondary alcohols and tertiary alcohols and mixtures thereof. In thepresent description, the term “secondary alcohol” refers to an alcoholhaving the formula

[0025] where R₁ and R₂, which may be the same or different, are eachindependently selected from the group consisting of an alkyl group whichmay be straight chain or branched in all isomeric forms having 1 to 20carbon atoms, preferably 1 to 10 carbon atoms, and aryl. The term “aryl”in this description refers to a phenyl-, or an alkyl-, nitro- orhalo-substituted phenyl group.

[0026] In the present description, the term “tertiary alcohol” refers toan alcohol having the formula

[0027] where R₃, R₄ and R₅ which may be the same or different are eachindependently selected from the group consisting of an alkyl group whichmay be straight chain or branched in all isomeric forms having 1 to 10carbon atoms, preferably 1 to 5 carbon atoms, and an aryl group. Thepreferred tertiary alcohols are t-butyl alcohol, pinacol andcholesterol.

[0028] Synthesis

[0029] The preparation of retinoid ester compounds can be accomplishedby a common general method, i.e. the conversion of the retinoid into itscorresponding chloride or anhydride followed by reaction with thealcohol. The process represents an application of the convergentsynthesis concept, which has been applied effectively for thepreparation of various esters.

[0030] The overall process for the synthesis of the t-butyl ester issummarized by the SCHEMES 1-5.

[0031] Thus, to the all-trans-retinoic acid 1 in ether, was addedN,N-dicyclohexylcarbodiimide, tert-butanol and catalytic amounts ofdimethylaminopyridine and the reaction mixture was stirred for 24 h atroom temperature to get the tert-butyl ester of retinoic acid (SCHEME1). tert-Butyl ester of all-trans-retinoic acid 2 was also obtained froman intermediate acid chloride. The intermediate acid chloride could beobtained by the usage of oxalyl chloride or thionyl chloride. Thus, theretinoic acid is treated with equimolar quantities of oxalyl chloride at0° C. to get the acid chloride and allowed to react in situ withequimolar amounts of pyridine and t-butyl alcohol at room temperature indark for 4-5 h SCHEME 2).

[0032] The ester can also be obtained by the reaction ofall-trans-retinoic acid with carbonyldiimidazole to get the reactiveimidazole which reacts with t-butyl alcohol to give the correspondingester (SCHEME 3).

EXAMPLE 1

[0033] (Scheme 2)

[0034] Preparation of all-trans-retinoic acid tert-butyl ester 2: To asolution of all-trans retinoic acid (100 mg, 0.33 mmol) in anhydrousether was added oxalyl chloride (42.3 mg, 0.333 mmol) at 0° C. andstirred at that temperature for 30 minutes and pyridine (28.7 mg, 0.363mmol), 2-methyl-2-propanol (26.8 mg, 0.363 mmol) was added and stirredat room temperature in dark after which time the reaction was completeas indicated by the TLC. The reaction mixture was then quenched withwater and extracted with ether (3×10 ml), saturated sodium bicarbonatesolution (3×5 ml) and again with water (3×5 ml), dried (MgSO₄) andevaporated. The thick residue was redissolved in hexane and applied onsilica Sep-Pak cartridge (2 g). Elution with hexane/ethyl acetate(9.7:0.3) provided the butyl ester of retinoic acid. Final purificationwas achieved by HPLC (10 mm×25 cm Zorbax-Sil column, 4 mL/min) usinghexane/isopropanol (90:10) solvent system. Pure all-trans retinoylbutyrate 2 (98 mg, 82.6%) was eluted at R_(v) 13 mL as a thick oil. ¹HNMR (CDCl₃): δ 1.034 (9H, s, t-Bu), 1.546 (3H, s, 20-CH₃), 1.719 (3H, s,19-CH₃), 2.021 (6H, s, 16 & 17-CH₃), 2.405 (3H, s, 18-CH₃), 5.784 (1H,s, 14-H), 6.150 (1H, d, J=5.61 Hz, 7-H), 6.170 (1H, s, 10-H), 6.304 (1H,d, J=4.43 Hz, 12-H), 6.335 (1H, d, J=5.49 Hz, 8-H), 7.105 (1H, dd,J=11.48, 15 Hz, 1 1-H); MS m/z (relative intensity) 356 (M⁺, 43), 342(96), 328 (23), 300 (98).

EXAMPLE 2

[0035] (Scheme 1)

[0036] A solution of all-trans retinoic acid (100 mg, 0.33 mmol),N,N-dicyclohexylcarbodiimide (74.2 mg, 0.36 mmol), 2-methyl-2-propanol(26.68 mg, 0.36 mmol) and 4-dimethylaminopyridine (0.12 mg, 0.001 mmol)in anhydrous ether (5 ml) was stirred at room temperature in dark(protected from light) for 24 hours under argon. The N, N-dicyclohexylurea formed was filtered and the filtrate washed with water (3×10 ml),5% acetic acid solution (3×5 ml) and again with water (3×5 ml), dried(MgSO₄) and evaporated. The solid residue was redissolved in hexane andapplied on silica Sep-Pak cartridge (2 g). Elution with hexane (10 ml)gave a small quantity of less polar compounds; further elution withhexane/ethyl acetate (9.7:0.3) provided the butyl ester of retinoicacid. Final purification was achieved by HPLC (10-mm×25 cm Zorbax-Silcolumn, 4 mL/min) using hexane/isopropanol (90:10) solvent system. Pureall-trans retinoyl butyrate 2 (22 mg, 18.5%) was eluted at R, 13 mL as athick oil. ¹H NMR(CDCl₃): δ 1.034 (9H, s, t-Bu), 1.546 (3H, s, 20-CH₃),1.719 (3H, s, 19-CH₃), 2.021 (6H, s, 16 & 17-CH₃), 2.405 (3H, s,18-CH₃), 5.784 (1H, s, 14-H), 6.150 (1H, d, J=5.61 Hz, 7-H), 6.170 (1H,s, 10-H), 6.304 (1H, d, J=4.43 Hz, 12-H), 6.335 (1H, d, J=5.49 Hz, 8-H),7.105 (1H, dd, J=11.48, 15 Hz, 11-H); MS m/z (relative intensity) 356(M⁺, 43), 342 (96), 328 (23), 300 (98).

EXAMPLE 3

[0037] (Scheme 3)

[0038] A solution of all-trans retinoic acid (100 mg, 0.33 mmol),carbonyldiimidazole (58.3 mg, 0.36 mmol) in anhydrous ether (5 ml) wasstirred at room temperature in dark (protected from light) for 2 hoursunder argon. The imidazole formed was then reacted with2-methyl-2-propanol (26.68 mg, 0.36 mmol) and stirred for 24 hours indark at room temperature. The reaction mixture was washed with water(3×10 ml), 5% acetic acid solution (3×5 ml) and again with water (3×5ml), dried (MgSO₄) and evaporated. The solid residue was redissolved inhexane and applied on silica Sep-Pak cartridge (2 g). Elution withhexane (10 ml) gave a small quantity of less polar compounds; furtherelution with hexane/ethyl acetate (9.7:0.3) provided the butyl ester ofretinoic acid. Final purification was achieved by HPLC (10-mm×25 cmZorbax-Sil column, 4 Ml/min) using hexane/isopropanol (90:10) solventsystem. Pure all-trans retinoyl butyrate 2 (18 mg, 15.1%) was eluted atR, 13 M1 as a thick oil. ¹H NMR (CDCl₃: δ 1.034 (9H, s, t-Bu), 1.546(3H, s, 20-CH₃), 1.719 (3H, s, 19-CH₃), 2.021 (6H, S, 16 & 17-CH₃),2.405 (3H, s, 18-CH₃), 5.784 (1H, s, 14-H), 6.150 (1H, d, J=5.61 Hz,7-H), 6.170 (1H, s, 10-H), 6.304 (1H, d, J=4.43 Hz, 12-H), 6.335 (1H, d,J=5.49 Hz, 8-H), 7.105 (1H, dd, J=11.48, 15 Hz, 11-H); MS m/z (relativeintensity) 356 (M⁺, 43), 342 (96), 328 (23), 300 (98).

EXAMPLE 4

[0039]

[0040] Preparation of all-trans-retinoic acid cholesterol ester (SCHEME4): To a solution of all-trans retinoic acid (100 mg, 0.33 mmol) inanhydrous ether (10 Ml) was added oxalyl chloride (42.3 mg, 0.33 mmol)at 0° C. and stirred at that temperature for 30 minutes and pyridine(28.7 mg, 0.36 mmol) and cholesterol (140.36 mg, 0.36 mmol) were addedand stirred at room temperature in dark for 16 h, after which time thereaction was complete as indicated by the TLC. The reaction mixture wasthen quenched with water and extracted with ether (3×10 Ml), washed withsaturated aqueous NaCl solution, dried (Na₂SO₄) and evaporated. Thethick residue was redissolved in hexane and applied on silica Sep-Pakcartridge (2 g). Elution with hexane/ethyl acetate (9.7:0.3) providedthe cholesterol ester of retinoic acid. Final purification was achievedby HPLC (10 mm×25 cm Zorbax-Sil retinoic acid cholesterol ester (103 mg,47%) was eluted at Rv 14 M1 as a thick oil. 1H NMR (CDCl₃): δ 0.7 (3H,s, 18′-CH₃), 0.85 (6H, d, 26′& 27′-CH₃), 0.9 (3H, d, 21-CH₃), 1.546 (3H,s, 20-CH₃), 1.719 (3H, s, 19-CH₃), 2.021 (6H, s, 16 & 17-CH₃), 2.405(3H, s, 18-CH₃), 4.625 (1H, m, 3′-H), 5.37 (1H, t, 6′-H), 5.78 (1H, s,14-H), 6.150 (1H, d, J=5.59 Hz, 7-H), 6.17 (1H, s, 10-H), 6.30 (1H, d,J=4.4 Hz, 12-H), 6.335 (1H, d, J=5.5 Hz, 8-H), 7.10 (1H, dd, J=11.48, 15Hz, 11-H); MS m/z 668, 369, 300.

EXAMPLE 5

[0041]

[0042] Preparation of all-trans-retinoic acid pinacol ester: To asolution of all-trans retinoic acid (100 mg, 0.33 mmol) in anhydrousether (10 mL) was added oxalyl chloride (42.3 mg, 0.33 mmol) at 0° C.and stirred at that temperature for 30 minutes and pyridine (28.7 mg,0.36 mmol) and pinacol (42.89 mg, 0.36 mmol) were added and stirred atroom temperature in dark for 16 h, after which time the reaction wascomplete as indicated by the TLC. The reaction mixture was then quenchedwith water and extracted with ether (3×10 mL), washed and saturatedaqueous NaCl solution, dried (Na2SO4) and evaporated. The thick residuewas redissolved in hexane and applied on silica Sep-Pak cartridge (2 g).Elution with hexane/ethyl acetate (9.5:0.5) provided the pinacol esterof retinoic acid. Final purification was achieved by HPLC (10 mm×25 cmZorbax-Sil column, 4mL/min) using hexane/isopropanol (90:10) solventsystem. Pure all-trans retinoic acid pinacol ester (103 mg, 47%) waseluted at Rv 16 mL as a thick oil. 1H NMR (CDCl₃): δ 1.2 (6H, s,2′-CH₃), 1.4 (6H, s, 1′-CH₃), 1.546 (3H, s, 20-CH₃), 1.719 (3H, s,19-CH₃), 2.021 (6H, s, 16 & 17-CH₃), 2.405 (3H, s, 18-CH₃), 4.625 (1H,m, 1′-CH), 5.78 (1H, s, 14-H), 6.150 (1H, d, J=5.59 Hz, 7-H), 6.17 (1H,s, 10-H), 6.30 (1H, d, J=4.4 Hz, 12-H), 6.335 (1H, d, J=5.5 Hz, 8-H),7.10 (1H, dd, J=11.48, 15 Hz, 1-H); MS m/z 400, 382, 300.

EXAMPLE 6

[0043] a. Experimental

[0044] The first test was to determine if the esterified compounds whengiven orally could restore normal growth of vitamin A-deficient rats.For this study, Sprague-Dawley, weanling rats were obtained from Harlan(Indianapolis, Ind.). They were fed the purified vitamin A-deficientdiet previously described (Suda et al., 1970, J. Nutr. 100:1049-152)supplemented with vitamins D, E and K (White et al., 1998, Proc. Natl.Acad. Sci. USA 95:13459-13464). When the animals stopped growing andbegan to lose weight, they were administered the indicated doses per daydissolved in Wesson oil. Controls were given the Wesson oil alone(vehicle group). The weight change over the 5-day study period wasanalyzed by ANOVA, followed by a matrix of pairwise comparisonprobabilities using four post-hoc tests when the overall P value wasless than 0.05. The post-hoc comparison tests included: Turkey HSDmultiple comparisons, Sheffe test, Fisher's least-significant-differencetest and the Bonferroni adjustment test. A result was consideredsignificant only if more than two post-hoc analyses resulted in aP<0.05.

[0045] The results of two experiments show that the t-butyl-RAderivative given at 83 pmoles/day (29.8 μg/day) supported growth over a5-day period that did not differ significantly from that of the groupfed an equal molar amount of atRA (25 μg/day). On the other hand, theanimals receiving no vitamin A (vehicle control) continued to loseweight as indicated in FIG. 1 (P<0.01 compared to atRA and thet-butyl-RA groups). When the compounds were given at 166 pmoles/day fora 5-day period, (50 μg/day atRA or 59.5 μg/day t-butyl-RA), the growthresponse of vitamin A-deficient rats was also equivalent, whereas, thevehicle-treated animals continued to lose weight (FIG. 2). FIG. 3summarizes these results in a bar graph that illustrates that thet-butyl derivative is as active as atRA in vivo.

[0046]FIG. 4 provides data obtained with the pinacol ester and thecholesterol ester. It shows that the pinacol ester has growth-supportingactivity in vitamin A-deficient rats as does the cholesterol ester, andboth compounds showed significantly enhanced growth compared to vehiclecontrol animals (P<0.05). However, whereas the growth of atRA-supportedanimals was superior to that of the cholesterol ester-fed group(P<0.05), the pinacol ester was intermediary in efficacy between thetwo, and did not differ significantly from either of these twocompounds. Thus, the pinacol ester is nearly equivalent to atRA inrestoring the growth of vitamin A-deficient rats, whereas thecholesterol ester is less effective.

[0047] Two independent toxicity studies were carried out with thet-butyl-RA derivative. FIG. 5 shows that 1 mmole/kg/day (300 mg/kg/day)of atRA produced severe acute weight loss over a period of 7 days aswell as other signs of toxicity (loss of appetite, hair loss, diarrhea).In contrast, the same molar amount of t-butyl-RA (357 mg/kg/day) enabledcontinued growth of the animals and revealed no other externally obvioustoxicity. In a separate study shown in FIG. 6, at equal molarconcentrations (1 mmole/kg/day for 5 days), t-butyl-RA showed noapparent toxicity, whereas atRA produced severe acute weight loss(P≦0.001) and outward symptoms of toxicity as described in the previousstudy. The toxicity of atRA was also illustrated by the reduction intestes weight that occurred in both experiments over the study period,whereas the t-butyl derivative showed no such indication (FIG. 7 anddata not shown). However, the difference in testes weights between theatRA and t-butyl-RA groups was not statistically significant due torather large biological variability.

[0048] Teratogenic activity of atRA is a serious drawback in itstherapeutic potential. We, therefore, determined whether the t-butyl-RAderivative could circumvent the teratogenic activity exhibited by atRA.The results of the study are summarized in FIG. 8 and Table 1. A singledose of atRA (0.1 mmole/kg or 30 mg/kg) given to pregnant rats atembryonic day 12.3 produced significant shortening of the ulna (FIG. 8)and resulted in skeletal abnormalities in 13 embryos out of a total of17 examined from four separate litters (Table 1). The control animalsreceiving the oil vehicle showed no abnormalities for the 18 embryosexamined from four separate litters. The t-butyl retinoid given at 0.1mmole/kg (35.7 mg/kg) also showed no abnormalities in 12 embryosexamined from four litters. However, when a 10-fold higher dose of thet-butyl derivative (1 mmole/kg or 357 mg/kg) was given, 10 of 13 embryosshowed abnormalities. The results of this experiment illustrate thatatRA is, indeed, teratogenic and that the t-butyl derivative shares thisliability, but only when given at a dose of 10 times higher than that ofatRA. Thus, there is a larger window of safety when using the t-butyl-RAderivative when compared to atRA.

[0049] b. Biological activity of the t-butyl ester or the cholesterolester or the pinacol ester in supporting growth of vitamin A-deficientrats.

[0050] Weanling male rats were obtained from the Harlan Company and werehoused individually in hanging wire cages and fed the vitaminA-deficient diet described previously (Suda et al., 1970). Atapproximately 70 days of age, the animals began to show a leveling offof growth and began to show weight loss. At this time, they were usedfor the following studies: They were given either 0.1 ml of Wesson oil(vehicle) or the indicated dose of atRA dissolved in the vehicle or oneof the derivatives at the indicated dose dissolved in the vehicle. Bodyweights were recorded daily and plotted as cumulative weight gain orloss over the study period as indicated on the graphs. A daily dose of83 pmoles (25 μg/day) of atRA is near the minimum amount needed toproduce normal growth in vitamin D-deficient rats as compared to thevehicle controls that continue to lose weight (FIG. 1). The t-butylderivative at the same molar dose (83 pmoles or 29.75 μg/day) showed agrowth response that did not differ from that of atRA over the 5 daytest period, but was significantly different from the vehicle oil group(P<0.01). When the dose was increased to 50 μg/day of atRA or 59.5μg/day of the t-butyl derivative, as expected, the growth response wasidentical. Thus, t-butyl-RA is equal to atRA in potency and efficacy,and can fully satisfy the growth requirement for vitamin A-deficientrats. FIG. 3 provides a summary of these results.

[0051]FIG. 4 provides data obtained with the pinacol ester and thecholesterol ester. These results clearly show that both the pinacolester and the cholesterol ester are able to support growth of vitaminA-deficient rats, with the pinacol nearly equivalent to atRA, and thecholesterol ester less so but nevertheless clearly much improved overthe vehicle control. These results illustrate that these two esterifiedforms provide atRA to support growth. We estimate that the pinacol esteris nearly as active as atRA and the cholesterol ester is perhapsone-third as active.

[0052] c. Assessment of the toxicity of atRA versus the t-butyl-RAderivative.

[0053] We next examined the actute toxicity of the t-butyl derivative ascompared to the atRA derivative in two independent trails. In theseexperiments, normal male rats weighing approximately 250-300 grams wereused. They were individually housed in cages and given Purina lab chowas well as water ad libitum. In the first study shown in FIG. 5, acomparison between the t-butyl derivative and the atRA derivativeillustrates that t-butyl-RA did not cause a weight loss whenadministered at 1 mmole/kg/day (357 mg/kg/day). This is an extremelylarge dose, and represents at least 3,600 times the amount of thet-butyl derivative needed to support a physiological growth response invitamin A-deficient rats. On the other hand, an equal molar amount (300mg/kg/day) of atRA produced a significant weight reduction (P<0.001) andsymptoms of vitamin A toxicity. When the experiment was repeated, weagain found that 300 mg/kg of atRA caused a severe weight loss comparedto the t-butyl-RA and vehicle groups (FIG. 6, P<0.001). On the otherhand, the vehicle control and the t-butyl derivative given at 1mmole/kg/day resulted in normal growth. Another indication of toxicityis testes weight as illustrated in FIG. 7. The testes weights of thevehicle and the t-butyl derivative were similar verifying that thisester did not cause overt toxicity, whereas a depression in testicularweight was observed with atRA given at 1 mmole/kg/day (300 mg/kg/day).

[0054] d. Teratogenic activity of atRA versus t-butyl-RA.

[0055] In this experiment, 19 female rats were obtained from SpragueDawley and were individually housed in cages and given purina chow aswell as water ad libitum. After approximately two weeks of acclimationto the animal facility, the females were placed with normal males on thesame diet, between 6:00 and 9:00 pm. The following morning, the femaleswere checked for vaginal plugs indicating fertilization. Vaginal smearswere then checked for sperm and when shown to be positive, the pregnantrat was placed in the study. At embryonic day 12.3 between 9:00 and10:00 in the morning, the rats received the following treatments givenas a bolus dose in oil orally. Four groups of rats received the vehicle;four received 0.1 mmole/kg (30 mg/kg) atRA in the oil vehicle; anothergroup received an equal molar amount (35.7 mg/kg) oft-butyl-RA; and afinal group received a ten-fold higher dose (357 mg/kg) of t-butyl-RA.The embryos were removed by cesarean section on day 18.5 and weighed aswell as checked for cleft palette. All embryos had approximately normalweight and no cleft palette was observed in any group. The embryos werefixed in 95% ethanol and a subset were randomly selected from eachlitter for staining to determine skeletal abnormalities. The onlyabnormalities observed at the 0.1 mmole/kg dose were markedly shortenedulnae in the atRA-treated group (FIG. 8). The results of this study showthat t-butyl-RA is less teratogenic than atRA. The t-butyl-RA derivativeis teratogenic when given at very high doses (1 mmole/kg), i.e. 10 timesthat of atRA (0.1 mmole/kg) where a similar percentage of skeletalabnormalities were observed (Table 1). We estimate, therefore, that thet-butyl derivative is approximately 10 times less teratogenic than atRA.TABLE 1 Teratogenic activity of atRA and its t-butyrate ester EMBRYOSTREATMENT abnormal/total examined vehicle  0/18 (0%) atRA (0.1 mmole/kg)13/17 (76%) t-butyl-RA (0.1 mmole/kg)  0/12 (0%) t-butyl-RA (1.0mmole/kg) 10/13 (77%)

[0056] Compounds

[0057] The present invention also provides compounds which are useful inthe treatment and prophylaxis of all diseases and disorders whereretinoid compounds have been shown effective, such as proliferative skindisorders characterized by abnormal cell proliferation or celldifferentiation (e.g. dermatitis, eczema, keratosis, acne and psoriasis)and they should provide especially useful for the treatment ofneoplastic diseases such as skin cancer, colon cancer, breast cancer,prostate cancer, lung cancer, ovarian cancer, neuroblastoma, andleukemia as well as skin conditions such as wrinkles, lack of adequateskin firmness, lack of adequate dermal hydration, and insufficient sebumsecretion.

[0058] These modified retinoid compounds are hydrolyzable in vivo to theparent retinoid, or analogs of the retinoid, over a period of timefollowing administration, and as a consequence regulate the in vivoavailability of the active retinoid, or analogs of the retinoid, therebyalso modulating their activity profile in vivo. The term “activityprofile” refers to the biological response over time of retinoidcompounds such as atRA or analogs of atRA. Individual modifiedcompounds, or mixtures of such compounds, can be administered to “finetune” a desired time course of response.

[0059] As used herein the term “retinoid” or “retinoid compound”encompasses compounds which a class of compounds consisting of fourisoprenoid units joined in a head-to-tail manner. All retinoids may beformally derived from a monocyclic parent compound containing fivecarbon-carbon double bonds and a functional group at the terminus of theacyclic portion. The term vitamin A should be used as the genericdescriptor for retinoids exhibiting qualitatively the biologicalactivity of retinol. This term should be used in derived terms such asvitamin A activity, vitamin A deficiency, vitamin A antagonist, etc.Examples of such retinoids were previously described and illustratedherein. As used herein the term “modified retinoid” or “modifiedretinoid compound” encompasses any retinoid in which one or more of thecarboxyl functional groups present in such retinoid are modified to forman ester by derivatization with a highly sterically hindered compound,which is preferably an alcohol. A “highly sterically hindered compound”encompasses compounds which have groups of significant size that areimmediately adjacent to the carbon atom containing the desiredfunctional group, e.g. alcohol or amino, and provides acarboxyl-modifying group that can be hydrolyzed in vivo so as toregenerate the carboxyl function and the original parent retinoid.

[0060] Structurally, the modified retinoid compounds having thedesirable in vivo bioactivity profile are ester derivatives of retinoidsand may be represented by the formula

R—O—R¹

[0061] where R is a retinoyl and R¹ is a highly sterically hinderedfunctional group selected from the group consisting of a first structurehaving the formula

[0062] where R₁ and R₂ which may be the same or different, are eachindependently selected from the group consisting of a straight chain orbranched alkyl group in all isomeric forms having 1 to 20 carbon atoms,preferably 1 to 10 carbon atoms, and aryl, and a second structure havingthe formula

[0063] where R₃, R₄ and R₅ which may be the same or different are eachindependently selected from the group consisting of a straight chain orbranched alkyl group in all isomeric forms having 1 to 10 carbon atoms,preferably 1 to 5 carbon atoms, and an aryl group.

[0064] The term “retinoyl” refers to a retinoid wherein the carboxylfunctional group (—COOH) of the retinoid is missing its hydroxyl (—OH)group. Thus, a retinoyl can be represented by the formula

[0065] Accordingly, R in the above formula may be a retinoyl of anyretinoid, and is preferably a retinoyl of a retinoid selected from thegroup consisting of

[0066] all-trans-retinoic acid;

[0067] 9-cis-retinoic acid;

[0068] 11-cis-retinoic acid;

[0069] 13-cis-retinoic acid;

[0070] 9,13-di-cis-retinoic acid;

[0071] TTNPB;

[0072] TTNN;

[0073] TTAB;

[0074] UAB8;

[0075] AM80;

[0076] AM580;

[0077] AM555S;

[0078] AGN 193836;

[0079] AGN 190299;

[0080] CD 2019;

[0081] CD 417;

[0082] R_(o) 48-2249;

[0083] R_(o) 44-4753;

[0084] R_(o) 10-9359;

[0085] SR 11254;

[0086] BMS 185354;

[0087] AGN 190299;

[0088] CD 437 (AHPN);

[0089] SR 11247;

[0090] SR 11217;

[0091] SR 11237;

[0092] AGN 191701;

[0093] LDG 100268;

[0094] LDG 100568;

[0095] LGD 100754;

[0096] R_(o) 25-7386;

[0097] BMS 188970;

[0098] SR 11004; and

[0099] SR 11203.

[0100] The preferred retinoyl is a retinoyl of all-tran-retinoic acid(atRA).

[0101] Any highly sterically hindered functional group or compound maybe used as substituent R¹ as long as it hydrolyzes in vivo to the parentretinoid and reduces the toxicity of the retinoid.

[0102] Preferred highly sterically hindered functional groups comprisestructures derived from secondary and tertiary alcohols such as tertiarybutyl (t-butyl) having the formula

[0103] as well as pinacol having the formula

[0104] and cholesterol having the formula

[0105] Three sterically hindered alcohol esters of atRA were synthesizedas previously described herein, namely, the t-butyrate ester (retinoylt-butyrate, also referred to herein as t-butyl-RA) having the formula

[0106] as well as the pinacol ester (retinoyl pinacol) having theformula

[0107] and the cholesterol ester (retinoyl cholesterol) having theformula

[0108] The above modified retinoid compounds may be administered to asubject in need thereof individually, in combinations of modifiedretinoid compounds, or in combination with other active pharmaceuticalagents, together with a pharmaceutically acceptable excipient, in apharmaceutical composition. As is well known, the modified retinoidcompounds may be present in a pharmaceutical composition to treat and/orprevent the previously mentioned diseases and disorders in apharmaceutically effective amount. For example, in a topicalformulation, the modified retinoid compounds may be present in an amountof from about 0.01 mg/gm to about 100 mg/gm of the composition. However,the modified retinoid compounds may be administered topically,transdermally, orally or parenterally, and typical oral dosages are fromabout 0.5 mg/day to about 5 g/day. The proportion of each of thecompounds in the composition is dependent upon the particular diseasestate being addressed and the degree of activity desired. In all cases,effective amounts of the compound should be used. In practice, thehigher doses are used where therapeutic treatment of a disease state isthe desired end while the lower doses are generally used forprophylactic purposes, it being understood that the specific dosageadministered in any given case will be adjusted in accordance with thespecific compounds being administered, the disease to be treated, thecondition of the subject and the other relevant medical facts that maymodify the activity of the drug or the response of the subject, as iswell known by those skilled in the art. In general, either a singledaily dose or divided daily dosages may be employed, as is well known inthe art.

[0109] For treatment and/or prophylaxis purposes, the compounds of thisinvention may be formulated for pharmaceutical applications as asolution in innocuous solvents, or as an emulsion, suspension ordispersion in suitable oils, solvents or carriers, or as creams,lotions, ointments, topical patches, pills, tablets or capsules,together with solid carriers, according to conventional methods known inthe art. Any such formulations may also contain otherpharmaceutically-acceptable and non-toxic excipients such asstabilizers, anti-oxidants, binders, coloring agents or emulsifying ortaste-modifying agents. The compounds may be administered orally,topically, parenterally or transdermally. The compounds areadvantageously administered by injection or by intravenous infusion orsuitable sterile solutions, or in the form of liquid or solid doses viathe alimentary canal, or in the form of creams, ointments, patches, orsimilar vehicles suitable for transdermal applications.

[0110] Compositions for use in the above-mentioned treatment andprophylactic uses comprise an effective amount of one or more modifiedretinoid compound as defined by the above formula as the activeingredient, and a suitable carrier. An effective amount of suchcompounds for use in oral formulations in accordance with this inventionis from about 0.01 mg to about 100 mg per gm of composition. However,the active ingredients may be administered topically, transdermally,orally or parenterally, and typical oral dosages are from about 0.5mg/day to about 5 g/day.

[0111] The formulations of the present invention comprise an activeingredient in association with a pharmaceutically acceptable carriertherefore and optionally other therapeutic ingredients. The carrier mustbe “acceptable” in the sense of being compatible with the otheringredients of the formulations and not deleterious to the recipientthereof.

[0112] Formulations of the present invention suitable for oraladministration may be in the form of discrete units as capsules,sachets, tablets or lozenges, each containing a predetermined amount ofthe active ingredient; in the form of a powder or granules; in the formof a solution or a suspension in an aqueous liquid or non-aqueousliquid; or in the form of an oil-in-water emulsion or a water-in-oilemulsion.

[0113] Formulations for rectal administration may be in the form of asuppository incorporating the active ingredient and carrier such ascocoa butter, or in the form of an enema.

[0114] Formulations suitable for parenteral administration convenientlycomprise a sterile oily or aqueous preparation of the active ingredientwhich is preferably isotonic with the blood of the recipient.

[0115] Formulations suitable for topical administration include liquidor semi-liquid preparations such as liniments, lotions, applicants,oil-in-water or water-in-oil emulsions such as creams, ointments orpastes; or solutions or suspensions such as drops; or as sprays.

[0116] Inhalation of powder, self-propelling or spray formulations,dispensed with a spray can, a nebulizer or an atomizer can also be used.The formulations, when dispensed, preferably have a particle size in therange of 10 to 100 μg.

[0117] The formulations may conveniently be presented in dosage unitform and may be prepared by any of the methods well known in the art ofpharmacy. By the term “dosage unit” is meant a unitary, i.e. a singledose which is capable of being administered to a patient as a physicallyand chemically stable unit dose comprising either the active ingredientas such or a mixture of it with solid or liquid pharmaceutical diluentsor carriers.

I claim:
 1. A retinoid ester having the formula R—O—R¹ where R is aretinoyl and R¹ is a highly sterically hindered functional groupselected from the group consisting of a first structure having theformula

where R₁ and R₂ which may be the same or different, are eachindependently selected from the group consisting of a straight chain orbranched alkyl group in all isomeric forms having 1 to 20 carbon atoms,and aryl, and a second structure having the formula

where R₃, R⁴ and R₅ which may be the same or different are eachindependently selected from the group consisting of a straight chain orbranched alkyl group in all isomeric forms having 1 to 10 carbon atoms,and an aryl group.
 2. The retinoid ester of claim 1 wherein R₁ and R₂are each independently selected from an alkyl group having 1 to 10carbon atoms.
 3. The retinoid ester of claim 1 wherein R₃, R₄ and R₅ areeach independently selected from an alkyl group having 1 to 5 carbonatoms.
 4. The retinoid ester of claim 1 wherein R¹ is a tertiary butylstructure having the formula


5. The retinoid ester of claim 1 wherein R¹ is a pinacol structurehaving the formula


6. The retinoid ester of claim 1 wherein R¹ is a cholesterol structurehaving the formula


7. The retinoid ester of claim 1 wherein R is a retinoyl ofall-trans-retinoic acid.
 8. The retinoid ester of claim 1 wherein R is aretinoyl of a retinoid selected from the group consisting ofall-trans-retinoic acid; 9-cis-retinoic acid; 11-cis-retinoic acid;13-cis-retinoic acid; 9,13-di-cis-retinoic acid; TTNPB; TTNN; TTAB;UAB8; AM80; AM580; AM555S; AGN 193836; AGN 190299; CD 2019; CD 417;R_(o) 48-2249; R_(o) 44-4753; R_(o) 10-9359; SR 11254; BMS 185354; AGN190299; CD 437 (AHPN); SR 11247; SR 11217; SR 11237; AGN 191701; LDG100268; LDG 100568; LGD 100754; R_(o) 25-7386; BMS 188970; SR 11004; andSR
 11203. 9. A retinoid ester having the formula


10. A retinoid ester having the formula


11. A retinoid ester having the formula


12. A pharmaceutical composition comprising a retinoid ester as setforth in claim 1 together with a pharmaceutically acceptable excipient.13. The composition of claim 12 having from about 0.01 mg to about 100mg of said retinoid ester per gram of the composition.
 14. Apharmaceutical composition comprising a retinoid ester having theformula

together with a pharmaceutically acceptable excipient.
 15. Thecomposition of claim 14 having from about 0.01 mg to about 100 mg ofsaid retinoid ester per gram of the composition.
 16. A pharmaceuticalcomposition comprising a retinoid ester having the formula

together with a pharmaceutically acceptable excipient.
 17. Thecomposition of claim 16 having from about 0.01 mg to about 100 mg ofsaid retinoid ester per gram of the composition.
 18. A pharmaceuticalcomposition comprising a retinoid ester having the formula

together with a pharmaceutically acceptable excipient.
 19. Thecomposition of claim 18 having from about 0.01 mg to about 100 mg ofsaid retinoid ester per gram of the composition.
 20. A method oftreating a disease characterized by abnormal cell proliferation or celldifferentiation comprising administering to a patient with said diseasean effective amount of a retinoid ester as set forth in claim
 1. 21. Themethod of claim 20 wherein the retinoid ester is administered orally,parenterally, transdermally or topically.
 22. The method of claim 20wherein the retinoid ester is administered in a dosage of from about 5mg to about 5 g per day.
 23. The method of claim 20 where the disease ispsoriasis.
 24. The method of claim 20 where the disease is cancerselected from the group consisting of skin cancer, leukemia, coloncancer, breast cancer, prostate cancer, ovarian cancer, neuroblastoma,and lung cancer.
 25. The method of claim 20 where the disease is a skindisorder selected from the group consisting of dermatitis, eczema andkeratosis.
 26. The method of claim 20 wherein the retinoid ester has theformula


27. The method of claim 20 wherein the retinoid ester has the formula


28. The method of claim 20 wherein the retinoid ester has the formula


29. A method of treating acne comprising administering to a patient withacne an effective amount of a retinoid ester as set forth in claim 1.30. The method of claim 29 wherein the retinoid ester is administeredorally, parenterally, transdermally or topically.
 31. The method ofclaim 29 wherein the retinoid ester is administered in a dosage of fromabout 5 mg to about 5 g per day.
 32. The method of claim 29 wherein theretinoid ester has the formula


33. The method of claim 29 wherein the retinoid ester has the formula


34. The method of claim 29 wherein the retinoid ester has the formula


35. A method of treating skin conditions selected from the groupconsisting of lack of skin firmness, wrinkles, lack of dermal hydrationand insufficient sebum secretion which comprises administering to apatient with one of said skin conditions an effective amount of aretinoid ester as set forth in claim
 1. 36. The method of claim 35wherein the retinoid ester is administered orally, parenterally,transdermally or topically.
 37. The method of claim 35 wherein theretinoid ester is administered in a dosage of from about 5 mg to about 5g per day.
 38. The method of claim 35 wherein the retinoid ester has theformula


39. The method of claim 35 wherein the retinoid ester has the formula


40. The method of claim 35 wherein the retinoid ester has the formula